The invention relates to a particle detector which combines the techniques of electrical impedance measurements and fluorescence from particles.
It is known to detect particles such as blood cells or yeast cells for example within a sample by passing the particle through a narrow orifice and detecting variations in the impedance across the orifice. Additionally, it is known to dye or stain samples with a suitable fluorescent dye and then illuminate the particles with a suitable light source such as a laser beam having a fundamental frequency, and thereafter determine the state of the particles by the fluorescence signal emitted from the particles.
However, such known systems are very complex, costly, require continuous adjustment and are limited in terms of minimum size of particles that can be detected. An object of the invention is to improve particle size and fluorescence particle detection systems. In particular, the invention seeks to enable use of a relatively narrow diameter orifice to provide accurate particle size measurements down to a small size whilst at the same time allowing fluorescence detection and preferably enabling detection and/or clearance of any blockages which might occur at the orifice.
According to one aspect of the invention there is provided a combined impedance and fluorescence particle detecting system comprising;
a plate separating a first and second chamber, the plate having a small orifice, preferably less than 150 microns in diameter, enabling the flow of particles between the chambers, and means for determining variations in impedance at the orifice due to the flow of particles therethrough;
a light source for irradiating the particles within or close to the orifice and a detector for receiving light emitted by the particles; and
Preferably means for clearing the orifice without removal of the plate from the system, and/or means for detecting orifice blockages is also provided. Other preferred features are set out in the attached claims and following description.